By Christopher ThornbergDebate about California’s housing crisis typically revolves around low-income households. The rule of thumb is that people shouldn’t spend more than 30 percent of their income on housing. But more than 90 percent of California families earning less than $35,000 per year spend more than 30 percent of their income on housing.

This isn’t new; that percentage has been stubbornly high for years. Nor is this an exclusively Californian problem — the comparable figure for the United States overall is 83 percent. What is new and disturbing is that the crisis is now spreading to middle-income households, families earning between $35,000 and $75,000 per year.In 2006, 38 percent of middle-class households in California used more than 30 percent of their income to cover rent. Today, that figure is over 53 percent. The national figure, as a point of comparison, is 31 percent. It is even worse for those who have borrowed to buy a home — over two-thirds of middle-class households with a mortgage are cost-burdened in California — compared to 40 percent in the nation overall.